Congenital and early onset binocular imbalance affect the visual maturation of 3-4% of U.S. infants. Even when treatment is successful in restoring clear media and good alignment, less than 1% of patients achieve normal stereoacuity and many develop amblyopia. During the previous grant period we established that minimizing the duration of misalignment in esotropic infants enhances binocular sensory outcomes. We will build on this work by assessing whether better binocular sensory outcomes are achieved with alignment before 6 months of age, if binocular sensory outcome is associated with long-term alignment and/or risk for amblyopia, if binocular sensory status at the onset of esotropia is predictive of long-term response to treatment, and whether surgical alignment of infantile esotropia places the infant at risk for accommodative esotropia. Our recent work with on nasal-temporal asymmetries in the motion VEP of patients with infantile esotropia has identified a close link between asymmetry and monofixation but the relationship with other asymmetries in eye movements and motion perception remain unclear. We will investigate relationships among asymmetries in motion VEP responses, OKN, motion perception, fusion, and stereopsis during normal maturation and in infantile and accommodative esotropia. These studies also will allow us to determine whether asymmetries precede or co-develop with tropia or whether they occur as a response to prolonged abnormal visual experience. The identification of the mVEP as an objective measure of monofixation during the previous grant period has set the stage for a series of studies that will address whether suppression is present at the earliest stages of esotropia, whether amblyopia develops in response to unequal suppression, and how suppression changes in response to treatment. The addition of a new paradigm, VEP dichoptic masking, will enhance the scope of these studies. Studies of the maturation of positional acuity in normal infants and pediatric patients with amblyopia will employ a broader range of positional tasks will be used to investigate the relationship between short-range and long-range deficits, the relationship between such deficits and recognition acuity deficits by which amblyopia is defined. In addition, we will continue working to build a battery of sensory tests for clinical trial outcome measures and for individual clinical assessment. These studies will help to define the necessary and sufficient conditions for the development of normal binocular vision and enhance treatment outcomes of pediatric patients. [unreadable] [unreadable]